It is well known that smoking is bad for you. But just how bad? Three new studies about cigarette smoking show it is more harmful than previously thought for both physical and mental health.

U.S. Surgeon General Regina Benjamin recently issued a statement on the impact tobacco smoke has on the human body.

"This report concludes that damage from tobacco smoke is immediate," said Benjamin.

Dr. Benjamin said smoke enters the blood stream quickly and affects every organ. She said even occasional smoking or breathing other people's smoke can lead to serious illness or death.

"One cigarette, or exposure to some second hand smoke, may cause a heart attack," added Benjamin.

Dr. Benjamin told people who are trying to quit not to give on up trying.

Smoking cigarettes is common in the military, especially in war zones. Military veterans who suffer from post traumatic stress disorder often turn to tobacco for help in regaining an even mood. That's what Walter Williams did when he served in Vietnam.

"I started to smoke in the military. It seemed to be what everybody was doing," recalled Williams.

Professor Miles McFall and Dr. Andrew Saxon from the Veterans Affairs Hospital in Seattle studied more than 900 veterans. Doctors treated half of the veterans for post traumatic stress syndrome (PTSD) while also treating them for their smoking habit. The other half were treated for PTSD but went to a separate program to quit smoking.

Saxon: "Veterans who received that integrated care, intervention, from their mental health clinician in the PTSD clinic, twice the number quit smoking as those who were referred to a smoking cessation clinic."

McFall: "There was no worsening of psychiatric conditions connected to quitting smoking."

In fact, a study from Brown University found quitting makes people happier. This study involved a group of 200-plus smokers who wanted to quit. They got a nicotine patch and counseling and then agreed on a quit date. Those participating in the study took a standardized test for symptoms of depression before the quit date and then at various intervals afterwards.

"Those people who were the most successful, who quit and stayed quit, came in with relatively low levels of depressive symptoms," said Professor Christopher Kahler who led the study.

In contrast, Kahler found that people who quit and then relapsed, were in better moods when they didn't smoke and then became depressed when they went back to smoking.

"If anything, people are feeling better when they are not smoking compared to when they are," added Kahler.

Kahler says he hopes the study inspires people to stop smoking, especially when they realize that quitting can lead to a happier, healthier life and not long-term deprivation.